1. Field of the Invention
The present invention generally relates to a positioning apparatus. More specifically, the present invention relates to a positioning apparatus, a positioning method, a positioning program, and a computer-readable recording medium for recording a positioning program.
2. Background Information
Conventionally, a SPS (Satellite Positioning System) apparatus has been used as a positioning system for positioning using manmade satellites. The SPS apparatus is constructed so as to determine its position by receiving signals from four satellites, for example. Specifically, the SPS apparatus performs positioning by selecting four SPS satellites from a large number of satellites located in the sky and receiving the signals therefrom. However, when the four SPS satellites selected by the SPS apparatus are close to one another, sometimes positioning precision deteriorates due to influence of signal noise or the like. Accordingly, in order to prevent the SPS apparatus from selecting such SPS satellites close to one another, DOP (Dilution Of Precision) values are used as shown in Japanese Patent Application Publication Hei-5-99680, especially FIG. 5 thereof. Japanese Patent Application Publication Hei-5-99680 is hereby incorporated by reference.
FIGS. 9A and 9B of the instant disclosure is a schematic explanatory view of the DOP values. In other words, FIG. 9A is a schematic explanatory view showing an example of a small DOP value, and FIG. 9B is a schematic explanatory view showing an example of a large DOP value. As shown in FIG. 9B, when the SPS apparatus selects SPS satellites S1 to S4 close to one another, the volume of a quadrangular pyramid formed by the four SPS satellites S1 to S4 becomes smaller and the DOP value becomes larger.
On the other hand, as shown in FIG. 9A, when the SPS apparatus selects SPS satellites S5 to S8 widely spaced from one another, the volume of a quadrangular pyramid formed by the four SPS satellites S5 to S8 becomes larger and the DOP value becomes smaller. Therefore, the SPS apparatus can improve the positioning precision by selecting SPS satellites S5 etc. that make the DOP value smaller.
However, even when the SPS apparatus selects SPS satellites to make the DOP value smaller, in cases of an environment having poor reception conditions for electric waves received from the selected SPS satellites, the positioning precision becomes lower, even though the DOP value is small. When the positioning precision worsens, the reliability of the DOP value deteriorating becomes a problem.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a positioning apparatus, a positioning method, a positioning program, and a computer-readable recording medium for recording a positioning program. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.